1. Field of the Invention
The present invention relates to ferritic and martensitic stainless steels having improved machinability by addition of nontoxic Cu.
2. Description of Related Art
Application of stainless steel to various industrial fields has been developed in response to remarkable progress of precision machinery industry and also gain of demand for electric home appliance, furniture and so on. In order to manufacture parts for such uses by automated machine tools with saving of labor, various proposals on improvement of machinability of stainless steels have been reported heretofore. For instance, machinability of ferritic stainless steel is improved by addition of Se as noted in SUS430F regulated under JIS4303. Machinability of martensitic stainless steel is improved by addition of Pb as noted in SUS410F and SUS410F2, or by addition of S as noted in SUS416 and SUS420F, each regulated under JIS4303.
However, the additive S substantially degrades hot-workability, ductility and corrosion-resistance and also causes anisotropy of mechanical property, although it is effective for machinability. Ferritic or martensitic stainless steel, which contains Pb for machinability, is un-recyclable due to unavoidable dissolution of toxic Pb during usage. Stainless steel 51430FSe regulated under SAE (corresponding to Type 430Se under AISI), which contains Se for machinability, actually causes environmental troubles due to toxicity of Se.